; phylum Chordata)
A subphylum that has a reliable fossil record from the Permian, and possible remains in Silurian sediments. Urochordates have tadpole-like larvae with notochords in their tails and a dorsal, tubular nerve cord, features that link them with the Chordata. The adults have a gelatinous or leathery protective test (the tunic) made from a chemical very similar to the cellulose found in plants. The tunic has two openings, allowing water to flow through the gill slits in the pharynx. The water flow is maintained by ciliated cells, and food is trapped by mucus on the pharyngeal gill slits.
Subjects: Zoology and Animal Sciences.